Return a topological ordering of a graph

## Problem: Output a topological ordering Given a directed graph with `n` nodes labeled `0..n-1` and a list of directed edges `edges`, return a topological ordering of the nodes. A topological ordering is a permutation of all nodes such that for every directed edge `(u, v)`, node `u` appears before node `v` in the ordering. ### Input - Integer `n` - List `edges` where each element is a pair `(u, v)` meaning `u -> v` ### Output - Return a list of length `n` containing one valid topological order. - If no topological order exists (graph contains a cycle), return an empty list (or explicitly signal failure). ### Constraints (reasonable defaults) - `1 <= n <= 2e5` - `0 <= |edges| <= 2e5` ### Follow-up - Explain how you would ensure the returned order is correctly produced (i.e., not just detecting that a topo sort exists, but actually outputting the sequence).